Method of making valve seat rings from a mixture of c,pb and a pre-alloy of fe-co-ni-mo by powder metallurgy

ABSTRACT

A POWDER METALLURGICAL METHOD OF MAKING VALVE SEAT RINGS HAVING A HIGH HEAT RESISTANCE, WHILE EMPLOYING A METAL POWDER WHICH IN ADDITION TO IRON CONTAINS FROM 0.5 TO 1% OF CARBON, FROM 0.7 TO 1.5% OF LEAD, FROM 1 TO 2% OF NICKEL, FROM 1.0 TO 2.0% OF MULYBDENUM, AND COBALT. AS STARTING MIXTURE IS EMPOLYED A PULVERIZED PRE-ALLOY WHICH CONTAINS FROM 1 TO 2% OF NICKEL, 1.0 TO 2% OF MOLYBDENUM, FROM 6.0 TO 7.0% OF COBALT, AND THE REMAINDER IRON. TO THE TUUS PRE-ALLOYED STEEL POWDER THERE IS ADDED CARBON IN QUANTITIES OF FROM 0.5 TO 1.0%, AND LEAD AT A QUANTITY OF FROM 0.7 TO 1.5%.SUBEEQUENTLY, THE MIXTURE IS BRIQUETTED, SINTERED COLD OR HOT POST-COMPRESSED, AND IF DESIRED, IS ANNEALED.

United States Patent Office 3,810,756 Patented May 14, 1974 METHOD OF MAKING VALVE SEAT RINGS FROM A MIXTURE OF C, Pb AND A PRE-ALLOY F Fe-Co-Ni-Mo BY POWDER METALLURGY Max Koehler, deceased, by Michael Koehler, Osterfeldstrasse 51, 5802 Wetter muhr) 4-Wengern, Federal Republic of Germany No Drawing. Filed Mar. 23, 1972, Ser. No. 237,504 Claims priority, application Germany, Mar. 24, 1971,

P 21 14 160.6 Int. Cl. 1322f 3/16, /00

US. Cl. 75-214 5 Claims ABSTRACT OF THE DISCLOSURE A powder metallurgical method of making valve seat rings having a high heat resistance, while employing a metal powder which in addition to iron contains from 0.5 to 1% of carbon, from 0.7 to 1.5% of lead, from 1 to 2% of nickel, from 1.0 to 2.0% of molybdenum, and cobalt. As starting mixture is employed a pulverized pre-alloy which contains from 1 to 2% of nickel, 1.0 to 2% of molybdenum, from 6.0 to 7.0% of cobalt, and the remainder iron. To the thus pre-alloyed steel powder there is added carbon in quantities of from 0.5 to 1.0%, and lead at a quantity of from 0.7 to 1.5 Subsequently, the mixture is briquetted, sintered, cold or hot post-compressed, and if desired, is annealed.

The present invention relates to a method of making valve seat rings by a powder metallurgical method, according to which an iron powder having added thereto carbon and lead, and other alloying constituents is briquetted, sintered, and subjected to a post treatment. This post treatment may consist either in a hot compression or in a cold compression at a pressure which exceeds the briquetting pressure. The heat compression or cold compression may be followed by a heat treatment according to which the workpiece is briefly heated to a temperature above the AC3-point whereupon it is quickly cooled and annealed at temperatures up to 650 C. If desired, prior to the cold compression, an additional heat treatment may be carried out.

A sliding and wear-resistant material for cylinder bushings and valve rings has become known which is produced according to the above mentioned method, and which for purposes of increasing its strength also contains from 1 to 4% lead, and nickel in quantities of from 0.5 to 5%, in addition to iron and carbon, which in the finished product is contained in quantities of from 0.5 to 1%.

For certain uses, for instance, when making valve seat rings for outlet rings of motor vehicles, it is necessary that the material in addition to the above mentioned strength properties also has an increased heat resistance which means it has suflicient heat resistance at temperatures up to 650 C. For outlet valves of motor vehicles, valve seat rings with increased heat resistance have been disclosed in US. Pat. 3,471,343, which are made of a pulverous mixture which prior to the above described treatment has the following composition:

from 0.8 to 1.5% from 1.0 to 4.0% from 0.5 to 5.0% of nickel,

from 1.2 to 1.8% of molybdenum, from 9.6 to 14.4% of cobalt,

and the remainder iron.

of graphite, of lead,

powder. The individual powders are mixed and are then briquetted at a pressure of approximately 3.5 tons per square centimeter and are subsequently at a temperature of approximately 1100" C. sintered in a neutral atmosphere for approximately three hours. The sintered workpieces are then cooled and are subjected to a cold compression at a pressure of approximately 12 tons per square centimeter, are heated for fifteen minutes to a temperature above the AC3-point, and then quickly cooled, and are annealed at a temperature of 580 C. for a period of thirty minutes. The Brinell hardness of the material is approximately 320 kilograms per square millimeter at room temperature and 205 kilograms per square millimeter at a temperature of 600 C. Valve seat rings made in conformity with this method thus have an increased heat resistance and can be used as outlet valves for motor vehicles. Practical tests of these rings which have proved very satisfactory, and which tests have been carried out on the test stand under full load have shown a useful running period of 250 hours.

It is an object of the present invention to improve the properties of the heretofore known valve seat rings having an increased heat resistance, in other words, to improve heretofore known valve seat rings containing nickel, molybdenum and cobalt, so that they will have an increased corrosion and erosion resistance and will also show an improved running behavior.

These and other objects and advantages of the invention will appear more clearly from the following specification and example. It has been found, surprisingly, that the above objects can be realized when the aforementioned alloy components are added to the starting mixture, not individually in the form of a powder, but when as starting mixture a pulverized pre-alloy is employed, which means a steel powder which contains the alloying components or ingredients.

With a method for making valve seat rings with increased heat resistance by a powder metallurgical method while employing a metal powder which, in addition to iron and carbon contains lead, nickel, molybdenum, and cobalt, the present invention consists primarily in that as starting mixture there is employed a pulverized pre-alloy which contains from 1 to 2% of nickel, from 1 to 2% of molybdenum, from 6 to 7% of cobalt, and the remainder iron, while the prealloyed steel powder has added thereto carbon in a quantity of from 0.5 to 1%, and lead in a quantity of from 0.7 to 1%, whereupon said mixture is, in a manner known per se, briquetted, sintered, cold or hot post compressed, and, if desired, is annealed.

The present invention furthermore provides that the pre-alloy from which the starting powder is made will, in addition to the above mentioned alloy components, also contain chromium in a quantity of from 1 to 2%, and titanium in a quantity of from 0.3 to 0.5%.

Tests with valve seat rings made according to the method of the present invention have proved that the employment of a prealloy instead of individual powders of the alloys components will yield rings which have a considerably improved running behavior with regard to heat resistance, corrosion resistance, and erosion resistance. Furthermore, a considerable increase in the heat withdrawal or heat deduction was ascertained. Whereas with running tests under full load, the heretofore known valve seat rings made with a powder mixture containing 12% cobalt failed after a running period of approximately 25 0 hours, which is rather high, motors equipped with valve seat rings according to the present invention have run still highly satisfactorily after a running period of 500 hours. This result was ascertained not only when employing lead-containing fuel, but also when employing lead-free fuel. This fact is of particular importance, because lead-free fuels are and will be employed more and more, in view of the ecology and the heretofore insert cast rings have an unsatisfactory life span when employing lead-free fuel.

It has furthermore been ascertained that when employing prealloys with a quantity of 12% cobalt, heretofore considered necessary, no improvement of the properties was obtained relative to rings which in conformity with the invention were produced with prealloys having a conten of from 6 to 7% cobalt. A reduction in the cobalt contents from 12% to a content of from 6 to 7% cobalt with heretofore known valve rings will, however, change the properties of such rings to such an extent that they could no longer be used for high load engines. This result is surprising and brings about that valve seat rings according to the invention with a content of only from 6 to 7% of cobalt can be used, where heretofore only rings with 10% cobalt of non-prealloyed powder could be used. The employment of prealloyed steel powder with a considerably lower cobalt content furthermore brings about a more uniform description of the individual alloying components and also results in a better diffusion of the carbon and therefore in an increase in the conductivity and in an improved corrosion and erosion resistance.

The present invention will now be described in connection with an example.

EXAMPLE As starting material for making valve seat rings there was employed a pulverized pre-alloy having the following composition:

With this prealloyed steel powder there were intermixed 0.8% of carbon and 1.2% of lead. The thus obtained mixture was then pressed into rings at a pressure of 3.5 tons per square centimeter. The thus obtained product was then sintered in a neutral atmosphere at a temperature of 1100 C. over a period of approximately three hours.

After the sintered rings had cooled, they were post compressed at a pressure of 12 tons per square centimeter and were heated for fifteen minutes to a temperature above the AC3-point and thereupon were quickly cooled. Subsequently, the rings were annealed for thirty minutes at a temperature of 650 C.

The thus produced rings showed an unexpected improvement with regard to corrosion, erosion, and heat resistance over valve seat rings which in customary manner were produced from a powder mixture with a cobalt content of 12%.

When employed in engines, an excellent running behavior was observed. After a running period of 500 hours under full load, the rings were still satisfactorily running even when employing lead-free fuel.

It is, of course, to be understood that the present invention is, by no means, limited to the specific example set forth hereinbefore, but also comprises any modifications within the scope of the appended claims.

What is claimed is:

1. In a powder metallurgical method of making high heat resistant valve seat n'ngs including the steps of providing a starting mixture of metal powders, briquetting, sintering and post-compressing said mixture, the improvement comprising: providing as said starting mixture, a mixture comprising 0.5 to 1.0% carbon, 0.7 to 1.5% lead and the remainder a pulverized prealloy consisting essentially of from 1.0 to 2.0% of nickel, from 1.0 to 2.0% of molybdenum, from 6.0 to 7.0% of cobalt and the remainder iron.

2. The method according to claim 1, wherein the sintered mixture is cold post-compressed.

3. The method according to claim 1, wherein the sintered mixture is hot post-compressed.

4. The method according to claim 1, which includes the step of heat treating the post-compressed sintered material.

5. The method according to claim 1, which includes the step of when preparing the starting mixture also adding thereto a quantity of from 1 to 2% of chromium and a quantity off rom 0.3 to 0.5% of titanium.

References Cited UNITED STATES PATENTS 3,471,343 10/1964 Koehler 29l82 X 2,381,023 8/1945 Wulif -213 X 2,368,282 l/l945 Wulff 75-213 X 2,352,316 6/1944 Goetzel 752l3 X CARL D. QUARFORTH, Primary Examiner R. S. SCHAFER, Assistant Examiner U.S. Cl. X.R. 

